There is a big difference -- bigger than people may realize. Some years ago Pearl switched from birch to maple as the wood of which their drums are constructed. Yamaha remains birch. Drum shells are made of several plies bent and then glued together.
Which wood is better? It's a matter of taste. The same theories and properties used to evaluate drum sounds in the world of drum sets apply to marching percussion. In general, maple is considered a slightly more premium grade of wood. It is harder than birch and yields more overtones and a wider range of dynamics. Birch is known for having far fewer overtones, less in the way of mid-range frequencies, and excellent projection.
When Pearl switched to maple I was skeptical it could work on the field. I didn't think they would project as well and that it would be more difficult to control their sound. In some respects I think these situations do hold true when compared with birch. It's just a matter of learning how to work with them. The result is that, in general, when you listen to corps using Pearl, the sound will be a little on the rounder side and will resonate more (which on an open field doesn't matter a whole lot, but still affects the particular sound). By contrast the Yamaha birch shells will be a little flatter, wetter, and punchier.
It's interesting: as a drummer I have long had a preference for birch toms because of their punchier, more controlled sound. But I prefer maple bass drums because that is where I want the rounder, more resonant sound. Yamaha has cleverly addressed the problem of the too-flat-sounding bass drum by creating a mixture of birch and mahogany plies on their bass drums. Brilliant thinking. Mahogany is more similar to maple in many respects, but darker.
I hope Madison stays with Yamaha because it is the sound I prefer. But Pearl makes one mean bass drum with those maple shells -- just check out any corps using them. It would be something else to hear the Cavaliers do their walk beat on Pearl Drums (sorry Yamaha, still love ya). Lastly I would like to say that tonal differences between these two wood types can be lessened through various tuning, tensioning, and dampening techniques. But I personally believe the differences are significant enough that if I were marching, a corps' use of birch tenors would be an important factor to me in my search for a corps. In other words, I'd probably prefer a Yamaha corps. But that's just my own preference. Both companies are tops in quality as far as I'm concerned.
Pearl's main series Championship series has always been maple, with the exception of the CSX snare drum, but that was a non free floating drum that was only in production for a few years, tenors and bass were made with maple as far back as i can remember atleast until 86, i ve'seen a few drums from 86 and they all had "all maple wood" on the logo badge.
the lower price Competitor series is made out of birch. but that series is for junior high, h.s. with a budget in mind.